1. Field of the Invention
This invention relates to a process for developing a lithographic printing plate using an aluminum plate as a support and utilizing a silver complex salt diffusion transfer process.
2. Prior Art
Some examples of a lithographic printing plate using the silver complex diffusion transfer process (the DTR process) are described on pages 101 to 130 of Andre Rott and Edith Weyde, "Photographic Silver Halide Diffusion Processes", published by the Focal Press, London and New York (1972).
As described therein, there have been known two kinds of lithographic printing plates using the DTR process, i.e., a two sheet type in which a transfer material and an image-receiving material are separated and a mono-sheet type in which these materials are provided on one support. The two-sheet type lithographic printing plate is described in detail in Japanese Provisional Patent Publication No. 158844/1982. Also, the mono-sheet type one is described in detail in U.S. Pat. No. 3,728,114, Japanese Patent Publications No. 30562/1973 and No. 15765/1976, and Japanese Provisional Patent Publications No. 111103/1976 and No. 150105/1977.
The mono-sheet type lithographic printing plate utilizing the silver complex diffusion transfer process with the use of an aluminum plate as a support (hereinafter referred to as "an aluminum lithographic printing plate") is described in detail in Japanese Provisional Patent Publications No. 118244/1982, No. 158844/1982, No. 260491/1988, No. 116151/1991 and No. 282295/1992, and U.S. Pat. Nos. 4,567,131 and No. 5,427,889.
In the above-mentioned aluminum lithographic printing plate, physical development nuclei are carried on a roughened and anodized aluminum support, and a silver halide emulsion layer which is substantially not cured is further provided thereon. A general process for making this lithographic printing plate comprises the steps of exposure, DTR development processing, water washing processing (washing off: removal of a silver halide emulsion layer with washing solution, hereinafter merely referred to as "washing processing") and finishing processing.
In detail, a metal silver image portion is formed on the a physical development nuclei by the development processing and the silver halide emulsion layer is removed by the subsequent washing processing to expose the metal silver image portion (hereinafter referred to as a "silver image portion"). Simultaneously, the anodized aluminum surface itself is exposed as a non-image portion.
After the washing processing, a finishing solution containing a protective colloid such as gum arabic, dextrin, carboxymethyl cellulose, polystyrenesulfonic acid, etc. is coated on the exposed silver image portion and the non-image portion for protecting the same. A processing of the so-called gum coating is applied to the surface of the plate. The finishing solution is also called as a fixing solution and it is general that it contains a compound which makes the silver image portion oleophilic such as a nitrogen-containing heterocyclic compound having a mercapto group or a thione group (hereinafter referred to as an "oleophilic agent").
In the aluminum lithographic printing plate, as described, for example, in Japanese Provisional Patent Publications No. 260491/1988, No. 116151/1991, etc., there is a problem that an electromotive force exists between the aluminum plate and the silver halide emulsion and causes corrosion at the silver image region by being developed by a developing solution having a high pH of 13 or so whereby pin-hole state spots which are so-called etch pits are caused. It has been known that this etch pit is likely caused when a silver halide emulsion with a high silver chloride content is used. The silver halide emulsion with a high silver chloride content has an advantage as compared with a silver halide emulsion with a high silver bromide content that it has a rapid DTR developing speed. An aluminum lithographic printing plate without etch pit has been desired to be developed while maintaining the so above advantage.
On the other hand, a plate making treatment is carried out by a processor (an automatic developer). In the processor, a developing step, a washing step, a finishing step and a drying step are provided, and a heater for controlling the temperature is generally provided at the developing step. With regard to the temperature of the developing solution, it is generally advantageous to set the temperature relatively high for controlling the temperature, assuming the high temperature at the summer season, has been carried out, for example, at 25.degree. C. as described in Example of Japanese Provisional Patent Publication No. 116151/1991. However, the temperature is set too high, there is a problem that the printing endurance is markedly decreased. Also, the number of etch pit caused is also increased. Accordingly, it has been desired to develop a processing process which can give a stable printing characteristic within the temperature range of 20.degree. C. to 30.degree. C.
Also, with regard to the developing time (a time from immersing the lithographic printing plate into a developing solution in a developing tank to the time of removing the silver halide emulsion layer at the next washing step), for example, in Japanese Provisional Patent Publications No. 116151/1991, No. 220763/1996, etc., it is disclosed that the development for 40 seconds in total is carried out including 8 to 10 seconds of immersing development in a developing solution and thereafter 30 seconds of diffusion transfer development in a system other than the developing solution. However, in general, when the development time exceeds a certain period, there is a problem that a printing endurance is lowered.
In U.S. Pat. No. 5,427,889, a DTR lithographic printing plate using an aluminum support having 500 or more of pits with a diameter of 0.03 to 0.30 .mu.m per 100 square .mu.m and an average diameter of the pits of 0.05 to 0.20 .mu.m. Moreover, in U.S. Pat. No. 5,405,730, a DTR lithographic printing plate using an aluminum support in which the total surface area of the depressed area is 50% or more based on the total surface area and the depressed area has a continuous depth of at least 0.5 .mu.m. However, even when these aluminum supports are used, their merits cannot sufficiently be utilized, and the above-mentioned problems are still retained.
Also, in DTR development of the lithographic printing plate at which the present invention is aimed, a thiosulfate is generally used as a solvent for the silver halide. However, the thiosulfate involves the problem of poor stability in an alkaline solution whereby decrease in the printing endurance due to running processing, etc. is caused Also, a waste solution (containing silver thiosulfate) after use of the developing solution which contains the thiosulfate will become a material to be regulated by a Law so that there is a problem that the waste must be controlled.